Members of the public in Denmark have recorded over 500 possible drone sightings in the past 24 hours, after Scandinavia was targetted in a series of aerial attacks that some European officials have linked to Russia.The population is full of fear following the drone incursions that shut down two of the country's airports on Wednesday night in what has been described by officials as a 'systematic operation' and a 'hybrid attack'. It was the second incident in two days following Monday night's drone disruption over Copenhagen airport that interfered with around 100 flights and left 20,000 passengers stranded.As officials continue to investigate who the 'professional actor' behind the attacks might be, civilians in Denmark are anxiously looking up at the skies in anticipation of more unwanted aerial incidents.The police are yet to confirm any of the 500 reported sightings, but are encouraging Danes to keep their eyes peeled and provide the authorities with detailed descriptions of anything they might see, reported TV 2. It comes as European ministers are scrambling to draw up plans for a continent-wide 'drone wall' to counter Moscow's aerial incursions, as the Kremlin warns that any strike on its aircraft would result in direct conflict with NATO. Nations including Denmark, Finland, Poland and the Baltic states will join Ukraine at a summit today to thrash out plans for what EU chief Ursula von der Leyen has described as 'the bedrock of credible defence.' The Kremlin has been accused of launching a campaign of hybrid attacks across Europe, exposing the vulnerability of the continent's airspace at a time of high tensions between Moscow and NATO.